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Improved Lightning Performance for 132 kV OHL

Tomas Ingemarson ; Johan Stelin
Göteborg : Chalmers tekniska högskola, 2017. 69 s. Diploma work - Department of Materials and Manufacturing Technology, Chalmers University of Technology, 2017.
[Examensarbete på avancerad nivå]

Lightning strokes to transmission lines causes a majority of the power quality issues that are so severe that sensitive industrial loads are disturbed. Historically Vattenfall concluded that it is too expensive to use shield wires for the 132 kV grid due to the high soil resistivity in Sweden. Today the situation is different with sensitive industrial loads and the current Vattenfall standard is to build portal tower with one shield wire. The shield wire is however not used to reduce the amount of lightning faults, it is used to ground the cross arm and reduce the amount of short circuits. In this project the lightning performance of different tower configurations used in the 132 kV grid is investigated using statistical insulation coordination in the softwares LPE and PSCAD. The optimal placement of the shield wires on towers located on flat ground is determined. Furthermore, the shield wire configuration of a new portal tower with two shield wires and typical Swedish conditions is proposed and compared to a portal tower with one shield wire. The demand is that the amount of lightning faults should be reduced by half compared to the case with a portal tower without shield wires. It is concluded that in order to achieve this decrease in the amount of faults a portal tower with one shield wire requires a tower foot resistance of 16.5 while a portal tower with two shield wires requires a tower foot resistance of 35.1. The distribution between single line to ground faults and short circuits for both configurations is estimated, where a second shield wire proved to reduce the amount of short circuits. Furthermore, it is concluded that every cross arm needs to be grounded properly in order to achieve the desired lightning performance. A cost estimation based on an average 132 kV line with average loading showed that a second shield wire could not cover its own costs. It is important to remember that the cost estimation is based on an average 132 kV line and it does not consider important industries or costs of groundings. If this would be included a second shield wire could be profitable in some cases. Therefore it is recommended to consider the local conditions when deciding if a new transmission line is built with one or two shield wires.

Nyckelord: Lightning performance, statistical insulation coordination, shield wire, portal tower, tower foot resistance, fault distribution, 132 kV.



Publikationen registrerades 2017-07-04. Den ändrades senast 2017-07-04

CPL ID: 250387

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